Renewable energy sources such as solar and wind power are well suited to distributed generation. However, renewable energy sources are too variable to use as a primary power supply without large and expensive battery banks to store and distribute power as required/needed. Accordingly, smaller renewable energy source installations are often utilized in urban/suburban environments to interconnect with the power grid to ensure 24×7 availability of power. Unfortunately, the practical arrangements required for such interconnects substantially reduces the efficiency of the total system.
For example, renewable energy sources (e.g., solar) may typically generate direct current (DC) energy. The energy required by the power grid is alternating current (AC) so that the DC power of the solar panel needs to be converted to AC. Small and medium-scale DC-AC inverters may average approximately 90% efficiency (older units may have efficiencies as low as 60%) so that approximately 10% of the generated energy is lost providing it to the power grid.
Electronics (e.g., computing systems) generally require DC power rather than typical power grid AC. Power supply units (PSUs) for electronic devices may employ a variety of conversion techniques to effect the conversion from AC-DC. The AC-DC conversion techniques may also impose losses. For example, PSUs for computers may have an efficiency range from approximately 70-85%.
For both AC-DC inversion and DC-AC rectification, efficiency also varies by load. At low (idle) loads losses are often much higher than at peak (design) load. When uninterruptible power supply (UPS) systems are also used these may impose further losses (e.g., approximately 0-20%).